1. Field of the Invention
This invention relates to an internal pressure explosion-proof construction for an electrically-driven robot which is used in an atmosphere in which there is a danger of exploding such as, for example, a robot for coating operation.
2. Description of the Prior Art
An internal pressure explosion-proof construction for an electrically-driven robot (hereinafter referred to simply as robot) is already known and disclosed, for example, in Japanese Utility Model Publication No. 59-160193 and Japanese Patent Laid-Open No. 61-14889 which corresponds to U.S. Pat. No. 4,732,526.
According to such conventional internal pressure explosion-proof constructions, an electric motor for driving an arm is installed in an airtight chamber formed in each arm of the robot, and the individual airtight chambers are connected with each other by means of a hose of the sealing type in which wires or conductors are accommodated.
Prior to operation of the robot, air or inert gas of a pressure higher than the atmospheric pressure is supplied into each of the airtight chambers by way of the hose in order to purge the airtight chambers of any explosive gas which may possibly be contained therein. In this manner, explosive gas around the robot is prevented from entering the airtight chambers.
With such an internal pressure explosion-proof construction as described above, however, since all of the airtight chambers in which the motors are installed are connected with each other by the hoses and/or air pipes, they make a single large airtight chamber as a whole. Accordingly, the airtight chambers in which explosive gas is contained cannot be purged efficiently, and it takes long time to purge. Further, the fact that no air discharging opening is provided individually for each of the airtight chambers contributes to the necessary a long time to purge.